Studies were conducted to investigate bacterial and fungal pathogens causing ulcer diseases in farmed and wild water bodies in Mymensingh during October, 2000 to September, 2003. Fishes were found to be affected by ulcer diseases, especially in the months' November to March usually peaked in January and February. Bacterial and fungal pathogens were isolated from the affected organs of the diseased fish and identified. The bacterial isolates were Aeromonas hydrophila, A. veronii biovar sobria, A. veronii biovar veronii, Pseudomonas fluorescens and Edwardsiella tarda and the fungal isolates were Aphanomyces invadans, Saprolegnia sp. and Achlya sp. In pathogenicity test, A. hydrophila was found to be more pathogenic than those of other isolates. In the case of fungi, A. invadans was detected as the most common fungal pathogen and was capable of producing characteristic lesion in the experimental fish. Experimental mixed infection with the bacterial pathogen, A. veronii biover sobria and fungal pathogen, A. invadans offered an interesting result producing similar lesions found in the naturally affected sampled fish. In histopathological observation, mycotic granulomas were a characteristic feature in the tissues of the EUS affected fishes. In contrast, no such feature was detected in the tissues of apparently healthy fish.